Self-assembly behavior of fluorocarbon-end-capped poly(glycerol methacrylate) in aqueous solution

Abstract

Well-defined perfluoroalkyl-terminated poly(glycerol methacrylate) (R F-PGMA) semitelechelics are prepared by atom transfer radical polymerization and copper(I)-catalyzed alkyne–azide cycloaddition reaction. R F-PGMA has a similar architecture as the well-studied perfluorinated poly(ethylene oxide) (R F-PEO) semitelechelics but bears two hydroxyl groups on each glycerol methacrylate unit. Because of the strong hydrophobic interaction of the perfluoroalkyl group, R F-PGMA semitelechelics self-associate to form core–corona spherical micelles in water above the critical micellization concentration (cmc) which depends on poly(glycerol methacrylate) (PGMA) content and temperature. For comparison, the R F-PEO semitelechelics with the same perfluoroalkyl terminal group as R F-PGMA are also prepared. The cmc values of R F-PGMA semitelechelics are found to increase with increasing temperature in water, which is opposite to the tendency of R F-PEO semitelechelics. According to the thermodynamic studies, the micellization process of R F-PGMA in aqueous solution is driven by both a negative enthalpy and an increase of entropy, whereas the micellization of R F-PEO is an entropy-driven process exhibiting a positive micellization enthalpy. This striking different behavior originates from intra-/intermolecular hydrogen bonds between the hydroxyl groups of the PGMA chains. These strong inter- and intramolecular hydrogen bonds between PGMA segments lead to a self-aggregation of R F-PGMA evident in temperature-dependent 1H and 19F NMR spectroscopy and dynamic light scattering measurements.